As an apparatus (method) of measuring a light environment with light from an illumination device or sunlight, a color luminometer that can measure illumination, correlated color temperature, and color rendering properties has widely been used. For example, the technique disclosed in Patent Document 1 provides a carriageable portable color luminometer that can be carried by a user and that enables measurement at any places desired by the user, regardless of a place where a measuring device is provided.
For illumination design, horizontal illumination (detail will be described later) received by a horizontal plane or vertical illumination (detail will be described later) received by a vertical plane such as a wall face is measured. For this, a method of horizontally or vertically providing the luminometer described in Patent Document 1 with a level gauge (level) is generally employed as a method of measuring horizontal illumination or vertical illumination.
This technique has problems such that (i) workability is poor since the level gauge (level) and the luminometer are different members, (ii) usability is unsatisfactory since a horizontal place is needed, and (iii) the measurement result is incorrect due to hand movement when illumination is measured with the luminometer held by a user.
On the other hand, according to the technology disclosed in Patent Document 2, a portable cabinet includes an illumination sensor irradiated with light and a tilt sensor that detects a tilt angle with respect to a reference attitude of the cabinet, and a method for deriving the illumination around the cabinet from the tilt angle of the cabinet detected by the tilt sensor and the value corresponding to the illumination detected by the illumination sensor, by using relation specifying means for specifying a relation indicating illumination around the cabinet and the relation specified by the relation specifying means, the tilt angle of the cabinet and a value corresponding to the illumination detected by the illumination sensor as being variables, is proposed.